1. Field of the Invention
The invention relates to the technical field of the preparation of crop protection agents.
2. Description of Related Art
It is already known from various publications that certain 3-alkylsulfinylbenzoyl derivatives have herbicidal properties. For example, in each of EP 2 167 473 A1, EP 2 127 521 A1, WO 2008/125214 A1, WO 2009/149806 A1 and WO 2011/012246 A1, 3-alkylsulfinylbenzoylpyrazoles are described as herbicides. In WO 2011/012247 A1, in each case 3-alkylsulfinylbenzoylcyclohexanediones are described as herbicides. WO 2011/035874 A1 describes N-(1,2,5-oxadiazol-3-yl)benzamides which carry, inter alia, a 3-alkylsulfinyl group in the 3 position of the phenyl ring. The preparation processes specified in these documents relate, for example, to a condensation process shown in scheme 1, in which a 3-alkylsulfinylbenzoic acid of the formula (I) is reacted with a compound of the formula (II) in the presence of a water-withdrawing agent, such as N-(3-dimethylaminopropyl)-N1-ethylcarbodiimide hydrochloride (EDCI), and optionally a cyanide to give the desired 3-alkylsulfinyl-benzoyl derivate of the formula (III).

In said scheme, the radicals have the following meanings: X1 is alkyl, X2 is various radicals, R*—H is in each case an optionally substituted 5-hydroxypyrazole or cyclohexanedione, n is 0, 1 or 2.
Furthermore, in some of the aforementioned documents, a preparation process as shown in scheme 2 is mentioned, in which, in a first step, the 3-alkylsulfinylbenzoic acid of the formula (I) is reacted with, for example, thionyl chloride to give the 3-alkylsulfinylbenzoic acid chloride of the formula (Ia) and this is then reacted with a compound of the formula (II) in the presence of a base and a cyanide to give the desired 3-alkylsulfinylbenzoyl derivative of the formula (III).

However, the processes known from these documents have a number of disadvantages. For example, in the process according to scheme 1, very expensive and toxic water-withdrawing agents are used. Since these agents are used not in catalytic amounts, but in equimolar amounts, moreover, large amounts of waste products are formed. The process shown in scheme 2 has the disadvantage that it only leads to a low yield of the desired 3-alkylsulfinylbenzoyl derivative of the formula (III). The factor responsible for the low yield is the lack of chemical stability, known to the person skilled in the art, of the 3-alkylsulfinylbenzoic acid chlorides of the formula (Ia), which are very quickly reduced to the corresponding 3-alkylsulfenyl-benzoyl derivatives. Furthermore, it is known, for example from “Nachrichten aus der Chemie, Technik and Laboratorium”, 1983, 31, 11, 892-896, that when attempting to prepare compounds of the formula (Ia) with the help of chlorinating agents, the chlorinating agent usually produces an unstable sulfinium chloride (Q), which does not lead to the desired product (III), but leads, in a Pummerer rearrangement, to the compound of the formula (W) (scheme 2b).
